The invention pertains to a process for the production of a moisture sensor of the type comprising two electrically conductive elements arranged on a dielectric substrate to form a sensor field which undergoes a change in impedance when wet.
Moisture sensors of this type and also methods for their production are already known. For example, in EP 0 507 491 A2, a process for the production of a rain sensor installed on a vehicle window is described. This sensor consists essentially of two electrically conductive surfaces intermeshing like fans, which are attached to a glass plate to form a resistance element. The change in the impedance of this resistance element caused by the presence of moisture on the surface of the sensor is recorded electronically and forms the sensor output variable. The two conductive surfaces consist of a metal oxide layer, which is deposited pyrolytically on the glass substrate. After the forming of the glass substrate, the final surface structure is produced by means of, for example, laser etching or a chemical etching process based on the use of a photomask.
A disadvantage of moisture sensors produced in this way is that the conductivity of the metal oxide layer, e.g., a layer of tin oxide, is significantly reduced by the forming process, normally carried out at about 600.degree. C., and by the following process of tempering the glass plate, and the sensitivity of the sensor is reduced.